1. Field of the Invention
This invention relates to automatic testing equipment (ATE) for dynamic testing of a microcomputer and specifically a microprocessor-based board. By a microprocessor-based board, it is meant a general-purpose central processing unit (CPU) or a special purpose microprocessor-based process controller, or the like, which is assembled in a self-contained package such as one or several circuit boards and is characterized by input and output terminals, (board edge inputs and outputs), at least one microprocessor unit (MPU), a bi-directional data and control bus coupled with the MPU, and at least some programmed logic functions (in either hardware or software form), and which is capable of performing complex system functions and executing instructions according to "intelligent", i.e., programmed, decision criteria. In particular, the invention is related to a technique for automatic operational (real-time) testing of a microprocessor-based board or system.
As the complexity of large scale integration (LSI) has increased and the applications for miniature and special purpose computers have expanded, the need for diagnosing errors in operational functions and faults in circuitry has also increased. Bus-connected LSI boards and MPU-based boards and systems have developed to such complexity that traditional testing is cumbersome and often impossible. While facilities and techniques for testing unprogrammed MPUs as well as LSI-type components, including random logic systems, are known to the art, such facilities and techniques have heretofore been inadequate for testing "intelligent" systems, such as programmed MPU-based boards or systems under actual operating conditions.
One difficulty in attempting to upgrade conventional ATE is the lack of facilities to automatically and sequentially search out and identify sources of errors and locations of faults within a bus-connected operating system. A second difficulty, which inhibits the diagnosis of faults, is the relatively limited access given the ATE to the internal operation of the system. The MPU-based board or system with its minimum component count and minimum number control and data lines represents a tremendously advanced system design. But, when such a system works improperly, i.e., requires debugging, the complexity of the debugging problem can defy diagnosis by previously known trouble-shooting techniques. There is thus a need for improved techniques and devices for automatically testing microcomputer-based boards and systems.
2. Description of the Prior Art
Logic testers for random logic systems are known. Many testers employ so-called spatial algorithms wherein faults are traced by physically isolating location. The application of spatial algorithms is generally limited to fault tracing of non-bus-connected random logic systems. Programmed components are typically isolated or removed from a tested system to simplify fault analysis.
Logic testers for some simple microprocessor-based systems are also known. Fluke Trendar of Mountain View, Calif., manufactures a line of microprocessor board testers utilizing nodal signature diagnostic and real-time comparative diagnostic techniques for testing of random logic boards, LSI-type boards and microprocessor-based boards. One such representative system is the Model 3040A. Testers and techniques have also been developed capable of testing complex and irregular LSI devices in real-time. A representative system is offered by Megatest Corporation of Sunnyvale, Calif. The level of complexity of a programmed microprocessor-based board, however, exceeds the current capability of these or other ATE to thoroughly analyze and detect faults. For example, known spatial algorithms are incapable of locating faults which create errors propagated through a programmed bus-connected system.
Therefore, with the increased availability and importance of microprocessor-based boards, there is an increased need for ATE capable of quickly and thoroughly diagnosing faults in complex programmed systems.